#string http\Header::negotiate(array $supported[, array &$result])

Negotiate the header's value against a list of supported values in $supported. Negotiation operation is adopted according to the header name, i.e. if the header being negotiated is Accept, then a slash is used as primary type separator, and if the header is Accept-Language respectively, a hyphen is used instead.

NOTE:
The first element of $supported serves as a default if no operand matches.

Params:#

• array $supported#
  The list of supported values to negotiate.
• Optional array &$result# Out parameter recording the negotiation results.

Returns:#

• NULL, if negotiation fails.
• string, the closest match negotiated, or the default (first entry of $supported).